Checking for Keys

Part of the Logic & Flow section of Coddy's Python journey — lesson 14 of 78.

When working with dictionaries, you often need to check if a specific key exists. Python provides simple ways to check for the presence of keys in a dictionary.

Using the in keyword:

my_dict = {'name': 'Alice', 'age': 30}

# Check if 'name' is a key in the dictionary
if 'name' in my_dict:
    print('Name exists in the dictionary')

# Check if 'city' is a key in the dictionary
if 'city' not in my_dict:
    print('City does not exist in the dictionary')

In this example, we use the in keyword to check if 'name' is one of the keys in my_dict. We also use not in to check if 'city' is not a key in the dictionary.

Using the keys() method:

my_dict = {'name': 'Alice', 'age': 30}

# Check if 'age' is in the keys
if 'age' in my_dict.keys():
    print('Age exists in the dictionary')

Here, my_dict.keys() returns a view object containing all keys in the dictionary, and we use in to check if 'age' is in that list.

Challenge

Easy

You are managing a dictionary of employee data, where each key is an employee's name and the value is their department. Your task is to:

Check if "Alice" is a key in the dictionary.
- If it exists, print: "Alice is in the company."
Check if "John" is not a key in the dictionary.
- If it does not exist, print: "John is not in the company."

Cheat sheet

To check if a key exists in a dictionary, use the in keyword:

my_dict = {'name': 'Alice', 'age': 30}

# Check if key exists
if 'name' in my_dict:
    print('Name exists in the dictionary')

# Check if key does not exist
if 'city' not in my_dict:
    print('City does not exist in the dictionary')

You can also use the keys() method:

# Check if key is in the list of keys
if 'age' in my_dict.keys():
    print('Age exists in the dictionary')

Try it yourself

employees = {"Alice": "HR", "Bob": "Engineering", "Diana": "Marketing"}

# Write code here

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Logic & Flow

1Variables Exploration

Constants Multiple Variable Assignments Swapping Variables Placeholder Variables Round Numbers List Casting

4Contact Book Application

Display Menu Add Contact

7Sets Part 2

Mathematical Operations Part 1 Mathematical Operations Part 2 Recap - Treasure Hunt Subsets and Supersets Iterating Over Sets Recap - Tournament Tracker

10Basic List Comprehensions

The Syntax Creating Simple Lists Adding Conditions Using Data Aggregation Recap - House Of Lists Recap - Elements Of Freedom

13Inventory Management System

Project Overview Add Item

Update Stock

Check Availability

Generate Report

2Dictionaries Part 1

What is a Dictionary?Creating a Dictionary Accessing Values Modifying Dictionaries Recap - Recipe Manager

5Advanced Decision Making

Ternary Operator Membership Checks Identity Checks Indentation Errors Recap - Vacation Filter

8Student Records Manager

Project Overview Add Student

11Advanced Functions

Returning Multiple Values Lambda Functions Part 1 Lambda Functions Part 2 Recap Challenge - Lambda Sort Recursive Functions Part 1 Recursive Functions Part 2 Recap - Sum Nested List

14Higher-Order Functions

The Map Function The Filter Function Recap - Email Validator Recap - Number Processor

3Dictionaries Part 2

Dictionary Methods Nested DictionariesChecking for KeysLooping Through Dictionaries Recap - Frequency Counter

6Sets Part 1

What is a Set?Basic Operations Set Methods Recap - Remove Duplicates

9Advanced Data Aggregation

Using Sum Finding Minimum and Maximum Sorting Data Efficiently Recap - Dictionary Sorter

12Basic Error Handling

What is Error Handling?The Try and Except Block Handling Multiple Exceptions Recap - Shopping Cart Errors

15Final Challenges

Smart Contact Manager Word Analytics Data Transformer